Vehicle interior rearview mirrors are commonly secured to either the header area near the top of the windshield or directly to the inside surface of the windshield in the forward vision area of the driver. Most have a ball member either extending from or into the mirror body to enable pivotal adjustment of the mirror. In one prior-known mirror having a ball member extending out of the mirror, the ball is captured in one end of a swaged tube. A helical compression spring is disposed in the tube and engages a disk which, in turn, engages the ball member. The disk has a portion which partially conforms to the shape of the ball. Often a similar structure is duplicated at the opposite end of the tube to connect the mirror to a mounting member. In addition, a cup member can be substituted for the disk. Such structures are disclosed, for example, in U.S. Pat. Nos. 3,367,616 to Bausch et al.; 3,635,435 to Perison, Sr.; 4,936,533 to Adams et al.; and 5,100,095 to Haan et al. Such "double ball" mirror support assemblies are typically fixed to the interior surface of the windshield.
A substantial number of other rearview mirrors are header-mounted mirrors. Examples of such assemblies are disclosed in U.S. Pat. Nos. 4,012,022 to Tomita; 4,066,235 to Hashiguchi; and 4,826,289 to Vandenbrink et al. In substantially each instance, a ball member extending from the mirror stay or support arm is received in a socket within the rearview mirror assembly itself, such socket being formed either by the mirror housing or by a pair of cooperating spaced apart plates. In either case, threaded fasteners draw the socket or spaced plates together within the mirror assembly to exert pressure on the ball to hold the mirror in a desired position. These fasteners are typically inaccessible for adjustment.
In each of the mirror assemblies described above, the clamping pressure on the ball is fixed at the instant it is assembled. As temperature increases or decreases, the clamping pressure changes as a direct result of the different coefficients of expansion and contraction of the materials. On one day, the ball joint may be stiff and difficult to adjust; while on other days the mirror may be loose and not stay in place.
Another disadvantage of the mirror assemblies described above is the inability to interchange mirror heads. When a ball pivot extends from the mirror mounting arm into the mirror housing, the housing must be specifically designed to accept that ball member on a permanent basis. Changing support arms for specific mirror heads and vice-versa without partial destruction of the mirror was impossible. Furthermore and related thereto is the inability to replace one of the components of the mirror assembly if it breaks; consequently, the entire mirror assembly is usually replaced. The desire to change mirror heads, stays, or replacement parts results in a replacement of otherwise perfectly good components and increases cost to the consumer.